Coating of Ti-6Al-4V alloy substrates with Ti/N compositional gradient films was carried out by reactive DC sputtering, to improve the blood compatibility of the alloy and to relax the stress concentrated at the interface. The compositional gradient was realized by varying continuously the nitrogen content in Ar-N-2 sputter gas during depositing. The deposited film appeared to be uniform and adhesive. TiN formation at the surface of the film was assumed, because of its yellow gold color and high hardness. Under SEM, it was found that the surface had fine particles dispersed on a smooth, accumulated deposit and that this depositing method improved not only the structural property of the film surface but also the adherence of the film with the substrate. Under AES, it was confirmed that nitrogen concentration in the film decreased gradually from the surface toward the substrate.